D flip-flops perfrom one of many major functions in finite state machines, which is typically a critical part of control logic. It is known that the control logic of a microprocessor can consume 20% of the processor's power. As more advanced architecture concepts, such as register renaming and out-of-order execution are implemented in a superscalar microprocessors, the control logic will likely become more complicated and its power dissipation will likely grow beyond the current level. In addition, to boost processor clock frequency, modern microprocessors typically adopt superpipelined execution which heavily utilise D flip-flops. Enhancing the speed of D flip-flops can enable a higher clock rate or allow more logic depth between two pipeline registers. These two objectives of low power and high speed provide a need in the art for circuits, such as D flip-flop circuits, which are energy efficient.